Insulation of electric wires and cables



March 10, 1931. F. J. BRISLEE LISULATION OF' ELECTRIC WIRES AND CABLESFiled April 9, 1930 N70/wiso thickness.

lPatented Mar. 10, 1931 UNITED STATES PATENT OFFICE FRANCIS JOSEPHBRISLEE, OF HUYTON, LANCASHIRE, ENGLAND, ASSIGNOR TO BRIT- ISH INSULATEDCABLES LIMITED, OF PRESCOT, LANCASHIRE, ENGLAND', A BRIT- ISH COMPANYINSULATION OF ELECTRIC 'WIRES AND CABLES Application led April 9, 1930,Serial No. 442,969, and in Great Britain February 9, 1929.

Some of the methods hitherto proposed for the utilization of esterifiedcellulose is the insulation of electric wires and cables yhave involvedthe application of this insu- 5 lation in the form of layers withtextile supporting layers and the maintenance of the laminated structureof the insulation thus produced in 4the finished insulation. The presentinvention is based on the discovery that by an appropriate treatment theseveral layers of such an insulation may be made to imite with eachother so that a non-laminated structure results.

Insulation having a laminated structure the kind indicated has beenproduced by applying esterified cellulose composition combined with atextile support, such as calico strips or cotton tape, wound around theconductor in layers to form the requisite In such insulation theesteriiied cellulose composition is subjected to a drying process so asto remove practically all the solvent before the insulation is appliedto the conductor. In another form of esterified cellulose insulation inwhich a laminated structure is also obtained, the textile support is inthe form of tubular braid surrounding the conductor and the esteriedcellulose composition is applied. by drawing the covered conductorthrough a vessel containing the composition in a solvent, after whichthe covered conductor is dried by passing it through a heated tube or byother f known methods in which a moderate temperature is employed fordriving oi practically all the solvent. This coating and drying process'may be repeated until the required thickness of composition has beendeposited on the braid and dried thereon. After this, a second braid isa plied and similarly coated with the esteri ed cellulose composition.This braiding and coating is repeated until the required thickness ofinsulation has been applied to the conductor. In both these forms, asusually produced, impregnation of the textile support b the esterifiedcellulose composition is not o tained. The composition is applied underapproximately atmospheric pressure to the surface of the supportand'does not penetrate through it.

In accordance with the present invention, I add to processes of the kindjust described, the further step consisting of heating the insulation tosuch a temperature that the esteriied cellulose composition (previouslyhardened by drying) is softened and becomes suiliciently plastic or Huidfor adjacent layers to unite and to penetrate or impregnate the textilesupporting materials embedded in or placed around the esteriiiedcellulose layers. After cooling, the resulting product is a solidinsulation possessing improved electrical and mechanical qualities ascompared with esterifed cellulose insulation produced by the knownprocesses described above.

Figure l is a view in section of an insulated electric cable before' theapplication of the heat treatment;

Figure 2 is a view similar to Figure 1 of an insulated electric cableafter the application of the heat treatment;

Figure 3 is a view in section of a rubbercovered insulated electriccable after the ap lication of the heat treatment.

As shown in Figure 1 the conductor l isl surrounded b layers of textilematerial 2, each one of w ich bears on each face a coating of esterifiedcellulose composition 3. This figure illustrates the condition of theinterior of the insulation prior to the application of the heattreatment in accordance with the present invention. It will be notedthat there is a definite laminated structure, each layer of esterifiedcellulose insulation with the enclosed textile support being scparatefrom the adjacent layers. Figure 2 illustrates the condition whichexists afterthe heat treatment. It will be noted that the laminatedstructure has disappeared, there being no separation between theadjacent layers of esterified cellulose insulation.

The invention is applicable both to cases Where the esterifed celluloseinsulation is applied directly to the bare conductor and to cases wheresome other insulating material is interposed.

The heat treatment may be given to the insulation after it has beenapplied to the conductr, or in some cases during its application. Wherethe removal of solvent has been effected by drying prior to the placingof the insulation on the conductor. The heat treatment consists inraising the temperature of the insulation to the neighborhood of 100o C.and maintaining it therefor a short period, suflicient to enable thesoftening and penetration and adhesion to take place. It may benecessary in order to complete these effects to raisethe temperaturesomewhat above 100o C. The heat treatment required need last only for acomparatively shorttime and the heating of the same portion may berepeated at intervals Without disadvantageous results. Accordingly it ispossible to heat each layer of tape or similar material just as itapproaches the conductor or just after it has been applied to thesurface so as to soften the coating and cause it to penetrate itssupport and adhere to the layer underneath.

Where the insulation has been applied in the form of strip or tape by acable Wrapping machine each strip after leaving its coil and immediatelybefore making contact with the cable may be heated by passing through ahot tube or over a hot surface which may be provided by a duct or guideplate which rotates With the other moving parts of the machine and ispreferably heatedy electrically. Alternatively. the heating may takeplace simultaneously with the Wrapping of the strip on the cable, aheated surface being pressed against the cable so as to have a kind ofironing action. As the layers are applied in close succession either ofthese methods of treatment will have the result that several adjacentlayers are simultaneously in the soft state and capable'of joiningtogether.

Vhere the 'heating takes place after the completion ofthe application ofthe insulation tothe cable; this may be done either as a continuousprocess by drawing the cable through a heating chamber or it may be doneas a separate step byplacing the coil of cable in a heating chamber. Forthe consolidation of the'layers of insulation by heat treatment afterapplication it Will probably beadvantageous in many cases to enclose theinsulation in such a Way that it cannot change its shape or dimensionswhen it softens. For this purpose the cable in the condition shown inFigure l can be covered with a lead sheath 4 applied in wellknown mannerbefore the heat treatment is eEected. After this treat-ment has beencarried out the lead covering may be removed, if it is not required toform .part of the completed cable. Instead of a lead sheath, one or moreWrappings of strong tape on the outside of the conductor may suiice forproducing the desired internal solidity of the insulation. Where thelead sheath is applied it may be provided that the heat contained in thesheath and transmitted by it to the in- The latter method is. only usedlsulation will suiice for the heat treatment of the insulation eithercompletely or in part. In the latter cases the sheathed cable may bedrawn through a heater as it leaves the lead press.

Where a layer of esterified cellulose insulation is used, in conjunctionWith a layer of rubber or other vulcanizable material (for Which theesteried cellulose may also provide a protective covering in some cases)the consolidation of the esteriied cellulose layer, by heat treatment,may take place simultaneously with the vulcanization of the rubber orother material enclosed Within it.

In providing a composite insulation of the kind above indicated, Weproceed by applying the rubber, or other vulcanizable material, to theWire or cable in any known manner, and then applying the esteriied'cellulose composition with a textile support or in sertion, by wrappingspirally or longitudinally tape or strip material over the outside ofthe vulcanizable insulation. After Which an outer covering, which may bea Wrapping or Wrappings of strong tape or a lead sheath, is applied toenclose the insulation and maintain its solidity during heating, theWireor cable is then heated in the manner usual for vulcanizing, andthereby the vulcanization and the consolidation are producedsimultaneously. After cooling this the vouter covering of tape or leadmay be removed if desire A cable of this kind is indicated in Figure 3where the conductor 1 is shown surrounded by an inner layer ofvulcanized rubber 5l and an outer layer of consolidated esteriedcellulose insulation 3 with the embedded textile supports 2. Y

' The esteriiied cellulose composition Will contain one or moreplasticizers, the action of which is of importance inobtaining theconsolidation of the layers of insulation by heat in'accordance with thepresent invention.

The following is van example of' a cellulose acetate composition in asolution appropriate for application by 'coating to a textile supportsuch as cot-ton tape or braid j Cellulose acetate 10 gms. Acetone 85ccs. Alcohol 8 ccs. Benzol 7 ccs. Triacetin 9 gms. Spirit nigrosine 0. 5gms.

In this the acetone, alcohol and benzol act as .solvents and4 theirproportions may be varied somewhat, and the alcohol and benzol may bereplaced by other solvents. The spirit nigrosine is a colouring agentand may be omitted or. replaced by another colouring agent according tothe requirements of the case. The triacetin is the plasticizer and may ibe replaced by other plasticizers either Wholly or part. Suitableplasticizers are z--dieste ys ulated electric conductor,

26 gms7 N itrocellulose syrup Butyl acetate 18. 5 ccs. Alcohol 22. 5ccs. Benzol 22. 5 ccs. Castor oil 7.7 ccs.

ln` this the alcohol and benzolact as solvents, the butyl acetate-andthecastor oil-are plasticizers. y ,o

A solution of the kind indicated is applied to the appropriate textilesupport which may be in the form ot strips or may be out up into stripsafter ooating and drying. lt is important that in the course of 'dryingall or nearly all of the solvent part of the mixture should beevaporated so-as to avoid a loss in volume of the insulation under thesubsequent heat treatment.A The thickness oat' the coating must soproportioned to the volume and form of the textile support that thecoating material can penetrate and lill all the interstices in thesupport when the heat treatment is applied.

llihat l claim as my invention and desire to secure by Letters Patent isl. A proce for the manufacture of an insulated electric conductor, whichcomprises applying insulation, embodying an esteriiied cellulosecomposition, under approximately atmospheric pressure, in layers roundthe conductor with textile supports, said insulamaterial round theconductor and Wrapping a further body of insulation, consisting oftextile tape having a dry hard coating of esteriied cellulose comosition, round the iirst body in a number o' layers, then heating theinsulated conductor to at least'100 C. to

' vulcanize the inner insulation and simultaneously consolidate theouter insulation by causing the esteriied cellulose composition tosoften and flow so that adjacent layers unite and the compositionpenetrates and impregnates the associated textile material forming thesupports.

' In testimony whereof I aiiix my signature.

FRANCIS JOSEPH BRISLEE.

tion being hard and substantially tree of solvent, and then heating theinsulation to a tempera-ture of approximately 100 at which thecomposition softens and flows so that adjacentA layers unite and theconnposiu tion penetrates and impregnates the associated textilematerial forming the supports, thereby consolidating the insulation.

2. A process for the manufacture of an in- Which comprises applying abody of vulcanizable insulating material round the conductor, and applying,1 a further body of insulation, consisting' oie an esteriiiedcellulose composition substantially tree of solventpwith textilesupports, round the outside orp the vulcanizable material in layers, andthen heating the insulated con ductor to a temperature oi at least 100to vulcanize the inner insulation and simultaneously consolidate theouter insulation by causing the esteriiied cellulose composition tosoften and :dow so that adjacent layers unite and the compositionpenetratesand impregnates the associated textile material iiorining thesupports.

3. A process for the manufacture or? insulated electric conductor,which. entreprises applying a body ot" vulcaniaable insulating sov

